Approximately one million plateletpheresis procedures are performed each year in the U.S., including 3,500 in the Platelet Center of the Department of Transfusion Medicine, NIH. Healthy donors are eligible to undergo plateletpheresis and leukapheresis procedures as often as 24 times per year. During plateletpheresis, citrate anticoagulant is added to the blood collection pathway to prevent clotting in the apheresis device, and is infused into the donor during the procedure. Adverse effects related to citrate administration are common, and include acute hypocalcemia due to the formation of calcium-citrate complexes. Recent studies in our Department indicate that changes in serum calcium, parathormone, osteocalcin, alkaline phosphatase, and vitamin D levels are also present and may be sustained for up to 24 hours after apheresis. In addition to volunteer plateletpheresis donors, the NIH Department of Transfusion Medicine maintains a registry of approximately 500 leukapheresis donors, who provide components for in vitro research use. These research apheresis procedures may involve processing twice as much blood volume (10 liters) as is processed in a typical plateletpheresis procedure (5 liters). Thus during leukapheresis, the total dose of citrate administered to the donor may be twice as great as that which occurs during plateletpheresis. Leukocyte and plateletpheresis donors may undergo more than 100 apheresis procedures during the course of their participation in the donor program at NIH. Donors are encouraged to take oral calcium carbonate supplements before or during apheresis if citrate related symptoms occur or have occurred in the past. The impact of serial, frequent, long-term apheresis donations on total body calcium balance and bone density is unknown. In this study, we performed bone density measurements (DEXA scans) of the wrist, lumbosacral spine, and hip in three cohorts of NIH donors (1) 50 long-term plateletpheresis donors who have undergone at least 50 plateletpheresis procedures at NIH in the past 10 years, (2) 50 long-term research leukapheresis donors who have undergone at least 50 leukapheresis procedures at NIH in the past 10 years, and (3) 88 age-, gender-, and race-matched whole blood donors, who have never undergone apheresis, as a control group. Comprehensive laboratory evaluations of the effect of citrate administration on bone metabolism and body calcium and magnesium levels before and after apheresis were also performed. The data indicate that apheresis induces an acute increase in parathyroid hormone, accompanied by a reduction in osteocalcin, and an increase in c-telopeptide and vitamin D levels. Some of these changes persist for as long as 4 to 14 days after apheresis. However, no adverse effects of apheresis on bone density could be found when comparing apheresis donors to whole blood donor controls. Mean T and Z scores, the conventional way of expressing bone density, were not significantly different among the two apheresis groups and among non-apheresis whole blood donors. There were trends for increased bone density in apheresis donors, consistent with anabolic effects of parathyroid hormone when released in a pulsatile, rather than a tonic fashion. Studies are continuing to allow recruitment of an adequately powered control (whole blood donor)group, and to include community Red Cross plateletpheresis donors who may donate up to 24 times yearly (versus 12 times yearly at NIH). The impact of prophylactic intravenous calcium supplementation during apheresis on bone density markers adn apheresis yields will be studied.